Chrome yellow



Patented Mar. 9, 1943 CHROME YELLOW Harry E. Bruce, York, Pa.

No Drawing. Application December 23. 1941, Serial No. 424,193

12 Claims. (Cl. 106-298) This invention relates to chrome yellows andhas for its principal object the provision of a process for so formingthe pigment color that it shall possess all of the advantages of thepresent pigments and in addition shall have a softer, texture and alower oil absorption.

A second object of the invention is to produce during said process, anintermediate product in which the heavy metal which is lead or zinc orsome other similar metal, is in solution in a form particularly suitablefor further treatment.

A third object of the invention is to produce lead, zinc, or similarmetals in solution for later treatment with a chromium compound such aschromic acid, potassium and sodium dichromates and an acid in order toproduce a chrome yellow without the usual plrvsical discomfort to theworkmen such as is characteristic of the use of strong acids normallyemployed, including acetic, nitric and sulfuric.

Other objects of the invention relate to details of the improvements inthe process and product as more particularly pointed out in the claims.The employment of these features reduces the time and-effortformerlyemployed in determining the gravity of each carboy of the nitric acidand insures that the maximum amount of litharge is converted into anactive lead compound,

etc. The lead solution produced according to the present invention ismore suitable for many uses and is more active in chemical reactionsthan is the usual lead acetate solution. Furthermore, the new leadsolution whether acid, neutral or basic can be made with less attentionto details and with the same maximum of lead in an active the tank orother container and it promptly disend of which time the acid is againpumped into solves the lead oxide that has. formed and also acts furtheron the ,metal compounds. This process is repeated until the solutioncontains the amount of lead desired and the solution is either acid,basic or neutral as may be desired for the next step.

The lead solution obtained by the process just described is moresuitable for many uses and is more active in a chemical reaction than isthe usual lead acetate solutions commonly employed, doubtless dueto thefact that the sulfamic acid which I use is highly ionized and gives highpH values approaching those of hydrochloric and sulfuric acid, whereasacetic acid is ever so much weaker and when in dilute solution is noteven able to dissolve the lead carbonate and thelead hydroxide formed intheold process. .Because of this it has been the practice previously toemploy very strong acetic acid and this is most disagreeable to theworkmen and its use slows up .in which I prefer to add the acid with thechromium solution and at other times addthe sulfamic acid after thechromium in desired form has state in a shorter period of time than thatrequired for'former methods.

My invention includes the use of amino-sulfonic acid which is commonlyknown at the present day as sulfamic-acid and is obtainable as a whitecrystalline solid which has little or no smell and is neither volatileor hygroscopic. As an example of my process I treat lead or leadcompounds with'sulfamic acid to produce the lead sulfamate. It is ofutmost importance'to cause a very large surface area of metallic lead tobe exposed to the acid and for this reason the lead is usuallyfeathered. I prefer to use only the very highest types of lead in thisprocess because the results justify the additional expense. The sulfamicacid is withdrawn from the container holding the metallic lead shapes inorder to permit the oxygen in the air to act upon the lead.

My preference is to expose the acid-treated lead to the air for a periodof about six hours, at the been added. The usual chromium compound iseither chromic acid, sodium dichromate or potassium dichromate.

Under certain conditions I employ a. heavy metal carbonate as a bufferto keep the solution from being too acid, in other words, to keep the pHfrom rising too high during the first period of reaction, then, as athird step, the chromium compound is added. As before, the times ofadding and the amounts of the variouscompounds will vary, according topreviously made plans, the depth of color which may range all the wayfrom pale' lemon to a deep red orange. the intermediate colors being forinstance, primrose, medium and the light oranges. I

Naturally instead of preparing the lead sulf amate solution directlyfrom the lead I may, and frequently do, purchase the lead oxide,dissolve this litharge in the sulfamic acid, making it acid, I

neutral or basic as may be desired, and I can do this in approximatelyhalf the time which previously was required to bring litharge intosolution as lead acetate. Not only is my solution far more active inchemical reactions than is the solution obtained by the use of aceticacid but my process requires very little care and brings into thesolution the same maximum amount of lead in an active state.

In the making of medium ormiddle chrome yellows, lead sulfate may bepresent but preferably only in minimum amount. My process avoids,entirely, the use of any sulfuric acid or aluminum sulfate or activesulfate ions, hence I can add or produce as little leadsulfate as I maydesire, because in my process'the s'ulfamic acid would govern theacidity of the reaction, thus entirely replacing the sulfuric acid orother substitute compound, such as the sharply acid aluminum sulfate,used for this purpose in order to minimize expenditure of the moreexpensive acetic acid in the former methods.

It is quite noticeable that the pigment colors formed by the use of,suli'amic acid with or without lead sulfamate have a softer texture andalso a lower oil absorption value, both of these being desirablequalities in a chrome yellow pigment color.

My process also eliminates the need for using nitric acid. In the oldprocess, since lead nitrate cannot be produced in the form of a basicsolution, the more expensive normal lead nitrate solution is employed,but this requires a very considerable care because for accurateprocessing it is essential that the amount 'of nitric acid usedshall becalculated for each and every batch ac.-

cording to determinations in the laboratory for the gravity of thenitric acid in each of the different carboys which have been furnished.In

this old process the lead nitrate reacts with the chromium compound andforms the lead chromate. ,The nitrate radical is caused to form morenitric acid which in turn reacts with the lead carbonate buffer to formmore lead nitrate which again reacts with the chromium compound incycles until the reactions are complete.

shades have all the usual good qualities of the nitrate yellows and havea better texture.

While I have described the process with particular reference to lead,obviously other heavy metals may be employed and the results are llygood. Other metals that may be used include antimony, bismuth, cadmium,tin and zinc. As a typical example of this when I mix zinc oxide,potassium dichromate and sulfamic acid in proper proportions thesupernatant liquid is very slightly colored, showing thatpracticallyallthechemicalshavereaetedtoformapigmentwhichisinsolubleinthis' top water whereas in the old process ofusing sulfuric acid there is always considerable coloration in thesupernatant liquid or top water. indicating that invariably a part ofthe chemicals are water soluble and are being washed from the pigmentwhich is produced.

What I claim is: I

1. The step in the process of producing a pigment having a yellow colorwhich consists in reacting a metal sulfamate with a chromium compound,the metal being taken from the group bismuth, antimony, tin, cadmium,1ead-and zinc,

and the chromium compound being taken from the group chromic acid,potassium dichromate and sodium dichromate.

2. The step in the process of producing a chrome yellow which consistsin reacting a chromium compound with lead sulfamate, and the chromiumcompound being taken from the group chromic acid, potassium dichromateand sodium dichromate.

3. The process of claim 2 in which sulfamic acid 'is present during thereaction.

4. The process of claim 1 in which the metal is zinc and the chromiumcompound is an alkali dichromate.

5. The process of producing a chrome yellow which consistsin reactinglead sulfamate with a chromium compound in the presence of leadcarbonate, the chromium compound being taken from the group chromicacid, potassium dichromate, and sodium dichromate.

6. The process of producing a chrome yellow which consists in reactinglead sulfamate with sodium bichromate in the presence of lead carbonate.

7. The process of claim 6 in which free sulfamic acid is present duringthe reaction.

8. The process of producing a chrome yellow which consists in dissolvinglead oxide in sulfamic acid, adding lead carbonate to the lead sulfamatesolution thus produced, adding a chromium compound and finally addingsulfamic acid, the chromium compound being taken from the group chromicacid, potassium dichromate, and sodium dichromate.

9. The process of claim 8 in which sulfamic acid is added during thestep of addingthe chro- 10. The process of producing a yellow pigmentwhich consists in causing a heavy metal to react mium compound.

with sulfamic acid, adding an alkali dichromate.

to the salt solution thus produced and adding sulfamic acid to thereacting solution in order to alter the pH of such solution so as toproduce the desired shade of yellow.

11. Theprocessofclaimloin whichthecarbonate of the heavy metal ispresent during the alkali dichrcmate'reaction.

1'2. Theprocessoiclaim 10 inwhich'themetal is zinc, and zinc carbonateispresentdurlng the alkali dichromate reaction. I

may a. sauce.

